A. Technical Field
The present invention relates generally to semiconductor light sensors, and more particularly to using various semiconductor fabrication and wafer level packaging techniques for fabricating miniature low power light sensors.
B. Background of the Invention
Light sensors are ubiquitous in modern society. Some applications use reflected light with optical detection for position sensing; these applications include bar code readers, laser printers and auto focusing microscopes. Other applications, such as digital cameras, cell phones and laptops, use optical sensors to gauge the amount of ambient light, and minimize the device's power consumption by regulating the intensity of the screen light as a function of the amount of the ambient light. Further, ambient-light sensors are integrated in laptops to adjust the screen's backlight to comfortable levels for the viewer. Light sensors may also be used in industrial applications.
Light sensors are typically implemented by fabricating a light-sensitive element, such as a diode, on the front side of a semiconductor wafer. In order to provide electrical or optical access, a traditional approach is to use wire bonding on the front side of the wafer. However, this approach requires significant semiconductor real estate and fan out resistance, resulting in a costly and high power consuming solution.
More recently, wafer level packaging (“WLP”) for light sensors have provided smaller size, higher performance and some cost reduction over conventional approaches. Also, there have been efforts to utilize through silicon vias (“TSV”), via passivation layer deposition, pad oxide opening, via filling, redistribution layer (“RDL”), solder bump formation, and dicing in order to reduce the size and improve the performance. Etching processing used to fabricate TSVs have included wet etching, RIE (reactive ion etching) and DRIE (deep reactive ion etching.) These efforts have provided some improvements, but the semiconductor techniques are still challenged by cost and power effectiveness. What is needed is a solution for light sensors that provides significant improvements in the size, cost, power consumption, as well as reliability.